Our invention relates to semiconductor devices in general and, in particular, to those known as Zener diodes or avalanche diodes operating on the principle of avalanche breakdown.
The Zener diode with its constant-voltage characteristic finds widespread use in a variety of electronic circuits such as those for producing reference voltage or for providing protective functions. One of the requirements for this type of diode is the constancy of the breakdown voltage. Breakdown should occur as far inside the semiconductor substrate of the diode as possible in order to make the breakdown voltage free from the influence of the insulating layer and the like on the semiconductor substrate.
Japanese Unexamined Patent Publication No. 57-71186 suggests a Zener diode (FIG. 1) explicitly designed for that purpose. This prior art diode was, however, unsatisfactory for the great temperature dependence of the breakdown voltage.
A diode has also been known (FIG. 2) which is practically free from the temperature dependence of the breakdown voltage. We also object to this second prior art device because its breakdown voltage is subject to fluctuations under the influence of the ions contained in the insulating layer and the plastic covering on the surface of the semiconductor substrate. We will later discuss in more detail the weaknesses of these prior art devices with reference to the drawings.